It is known that a heat exchanger exchanges heat between a gas and a refrigerant more efficiently when the gas flows through spaces between exchanger surfaces that are narrow. In addition, more exchange surface can fit into a given volume if this spacing is narrow.
It is also known that, when the gas being cooled contains moisture, narrow spaces are far more prone to icing-up than when spaces are wide. Narrow-spaced heat exchangers are therefore often avoided when moisture-containing gasses, such as air, are to be cooled with coolant or refrigerant at, or below, the freezing point of water.